An air turbine starter (ATS) is typically used to start an aircraft turbine engine, for example, a gas turbine jet engine. The ATS is typically mounted to the jet engine through a gearbox or other transmission assembly and a cover plate or wall is located between the starter and gearbox housings. The gearbox transfers power from the ATS to the engine to start the engine.
Many air turbine starters typically include lubricants, such as oil, to run properly. The lubricants are prevented from entering one or more areas of the gearbox or starter via one or more seals. In one exemplary gearbox configuration, a pressurized (or buffered) seal that is fed with a high pressure stream of air, for example, a labyrinth seal, is used to prevent oil from undesirably flowing out of the gearbox. Although this type of seal is generally effective, air flow from the pressurized seal may affect the ability of the ATS to maintain lubricant within its interior. This is particularly noted in configurations in which ATS seals, such as clearance seals, are used to keep lubricants inside the ATS.
Turning to FIG. 1, a section of one such exemplary embodiment of an air turbine starter is shown. The section of the air turbine starter 100 shown includes an output shaft 102, a stator plate 104, drive shaft 106, and a clearance seal 108. The output shaft 102 is configured to couple to a gearbox 110 and to the drive shaft 106. The drive shaft 106 is generally a hollow cylinder and includes an end 114 that is generally flat and that has an opening 112 that allows the drive shaft 106 to at least partially mate with the output shaft 102. The stator plate 104 includes a shaft opening 118 that is defined by an inner wall 120 and that has a diameter sufficient to receive the drive shaft 106 and provide a gap between the stator plate 104 and drive shaft 106. The clearance seal 108 is press fit to the drive shaft 106. The clearance seal 108 forms a small clearance or plurality of small clearances between the seal 108 with the drive shaft 106 to create pressure differentials and air and oil flow patterns between the clearances that prevent leakage from the ATS 100 to the gearbox 110.
It has been found that when the exemplary ATS 100 of FIG. 1 is joined to a gearbox that uses the pressurized seal described above, a portion of the high pressure air, indicated by arrows in FIG. 1, may be diverted into the opening 118 between the stator plate 104 and the drive shaft 106. The high pressure air may cause disruption of the airflow patterns of the clearance seal 108, which in turn may cause oil from the ATS 100 to leak through the clearance seal 108. As a result, the clearance seal 108 may not operate as intended, and/or the ATS 100 may need to undergo more frequent maintenance.
Therefore, there is a need for an improved ATS that can operate more efficiently, and/or undergoes less maintenance and/or does not cause a clearance seal to leak fluid when operated with a pressurized seal. The present invention addresses one or more of these needs.